The present invention relates generally to a joint prosthesis. More particularly, the present invention relates to a joint implant designed to replace the inter-phalangeal or metatarsal-phalangeal joints in the foot, or the inter-phalangeal or metacarpal-phalangeal joints in the hand. In addition, the joint implant may be scaled up to replace any linear joint between adjacent long bones.
Joint implants for replacing finger and toe joints are well known. For example, U.S. Pat. No. 4,246,662 describes a prosthetic joint comprising a one-piece body of flexible physiologically inert material having an enlarged central portion with two stem portions extending from opposite sides of the enlarged central portion. The enlarged central portion contains a slot which extends substantially through the central portion thereby forming a hinge for articulation of a joint. U.S. Pat. No. 4,313,232 discloses an elastomeric joint prosthesis for replacing damaged joints in humans. The joint prosthesis is substantially elongate with oppositely tapered ends and a wider central segment. The joint prosthesis is made of a biocompatible cloth mesh which is reinforced with an elastomer to provide lateral stability and enable the prosthesis to flex along a single plane. Bending occurs along a plane in the wider central segment of the blank. U.S. Pat. No. 4,634,445 describes a small joint spacing prosthesis having an elongate silicone rubber body which contains a Dacron or nylon string for reinforcement. The prosthesis further comprises a spherically shaped spacer in its middle having flat end faces for abutment with bone ends, and intramedullary stems extending from opposite sides of the spacer which are of lesser width than the spacer. The spacer and intramedullary stems comprise one continuous body. This patent also discloses that the bending of the joint prosthesis occurs in each of the stems and not in the spacer.
Therefore, there are no presently existing joint implants which form a structure comprising an elongated solid stem cylinder with a spacer which fits loosely over the cylinder thereby enabling the stem cylinder to flex during articulation of a joint at the point of the spacer, using the spacer as a fulcrum, but without substantial bending of the spacer.